Sculpting smooth model with jaggered vertex
I'm by no means an expert but when sculpting this can occur quite frequently, ideally you use dynamesh and smooth it to prevent the pinches from forming in the first place but if it can't be helped you could select the area from edit mode wireframe (mind the backside of the model), weld all the verts so it's a flat surface, dynamesh and continue. There are probably better solutions, but this is how I've figured to solve it.